Piping systems are typically anchored to, or supported by building structures such as walls, floors, or ceilings, at one or more locations. The systems are also anchored to building structures to inhibit movement of the piping system during a dynamic event, such as an earthquake or fluid flow through the pipe. Pipe movement may also be due to the phenomenon known as "water hammer" or objects impacting the piping system.
Piping systems are also subject to temperature changes, which cause thermal expansion, and thus displacement of the piping system. Prior restraints designed for normal support and/or dynamic events may be too restrictive of pipe movement during thermal expansion, and thus result in an over-stressed condition in the piping system or imposition of unacceptable loads on the piping or associated equipment.
Piping systems are also subject to low frequency vibration caused, for example, by rotating equipment associated with the systems, turbulent fluid flow through the systems, or chatter in valves forming part of the system. Pipe restraints designed to react to dynamic loads and thermal expansion do not provide damping for vibration loads.
One attempted solution to these problems has been the use of snubbers. Snubbers allow the piping to freely expand but momentarily restrain the piping system during a dynamic event. However, snubbers have been found to be complex, require maintenance, and have a history of failure, which has resulted in costly inspection programs, especially in the nuclear industry.
Another attempted solution has been the use of gapped supports. Gapped supports allow the piping system to move freely within a predefined area, but rigidly prevent movement of the piping system beyond the boundaries of this area. The problem with gapped supports, though, is that high impact loads are typically imposed upon the piping system and other structures when the piping system reaches a boundary of the predefined area during a dynamic event.
Other attempted solutions have been the use of energy absorbers. For example, U.S. Pat. No. 4,620,688 discloses the use of steel plates, which plastically deform to absorb energy. The problem with the steel plate solution is low cycle fatigue life, requiring frequent replacement of the devices. Another solution is that disclosed in U.S. Pat. No. 4,955,467, in which energy is absorbed by friction. However, a major drawback with this solution is the large amount of variability in the resulting friction force.
In yet another solution, shown in U.S. Pat. No. 5,240,232, loops of wire rope are attached to first and second slide members, which allows movement of the piping system while absorbing energy. This solution, though, has been found to be complex, requiring slide members, and centering bushings, and further subjects the device to undesirable bending loads.
In a prior copending application, a solution is disclosed in which first and second displacement members connect to opposing portions of a helical coil composed of wire rope. One of the displacement members is connected to a piping system, and the other displacement member is connected to a supporting structure. The coil then flexes as displacement loads are applied, for example, by thermal expansion of the piping system, where inhibiting relatively large movements of the piping system caused by dynamic events. However, if the displacement members displace too far relative to one another, the coil tends to collapse, which limits their utility. Collapse of the coil can be prevented by employing movement-limiting stops, but at the cost of increased complexity and weight. The present invention provides an improved wire rope restraint that resists collapse when a severe displacement load is applied.